1. Field of Invention
This invention relates to luminaires in general, and to lightweight, field-assembled luminaires for suspended ceilings in particular.
2. Description of Prior Art
Current fluorescent luminaires are connected to the utility power line via conduit, BX, or Romex type cable. Since the fluorescent luminaire is connected directly to the utility power line via a 15 or 20 amp branch circuit, the luminaire must be designed to enclose and protect the input leads to the fluorescent lamp ballast, the lamp sockets, and the interconnecting leads between the ballast and the lamp sockets. In order to provide the necessary protection, fluorescent luminaires are made out of relatively heavy gauge steel to meet specific standards set by Underwriters' Laboratories (UL), such as, UL1570. UL requires that heavy gauge metal be used to insure that the luminaire can withstand a certain degree of abuse without exposing leads, electrical components, the ballast, current carrying parts or devices with exposed metal which could constitute a shock or fire hazard.
Due to the structural requirement set out in the UL standard a typical 2.times.4 foot luminaire can weigh over 30 pounds and a 2.times.2 foot fixture can weigh over 15 pounds. Since current luminaires act as electrical enclosures for the fluorescent ballast and the interconnecting leads, raceway covers (also made out of heavy gauge steel) are provided to contain the potentially hazardous wiring. Luminaires, currently on the market, often contain 25 to 30 stamped metal parts plus the fasteners to hold them all together.
Because these luminaires contain such a large number of parts, they are assembled in factories, where they are packaged in individual boxes. Then they are loaded onto trucks, shipped to and stored in warehouses. They are then loaded onto different trucks and delivered to lighting wholesalers and retailers or job sites where they are stored until they are installed. In each case, the luminaires occupy a significant amount of floor space and volume.
Once at the job site the luminaires are lifted overhead into position within the ceiling grid. This is no easy task since each 2.times.4 luminaire can weigh 30 pounds or more. The grid system and the supporting wires are required to be sufficiently strong to accommodate this extra weight.
Fluorescent lamp ballasts currently in production are designed to operate from 15 or 20 amp branch circuits, which are typically 120, 240, or 277 volts; 60 Hertz. Due to the high energy levels available from these branch circuits, the lines connecting the input to the ballast to the branch circuit is required by the local electrical code to be run in conduit, BX, or Romex. The output leads connect the ballast to the lamp sockets and supply voltages and currents which do not meet the limits of the National Electrical Code requirements for either Class II or Class III wiring. Therefore, this wiring too must be provided with special protective encasement by the luminaire. This is generally accomplished by designing wire raceways in the luminaire to meet special requirements established by Underwriters Laboratories.
The ballasts currently in production are either magnetic ballasts or electronic ballasts. The input power is provided from 50 or 60 Hertz line voltage and the output of the ballast is connected to a lamp socket or sockets via interconnect wiring. The magnetic ballast generally consists of a transformer with a current limited output and a power-factor correction capacitor connected across the input. Since the magnetic ballast is operating at 60 Hertz, the size of the metal can of a ballast capable of handling 60 watts of output power is 2.25" wide by 1.5" high by 8" long and weighs about 3 pounds. Electronic ballasts are generally manufactured in the same size package but weigh 1.25 to 2.5 pounds.